Polymer based sensors for detecting agricultural analytes and methods of making same

ABSTRACT

A polymer-based sensor for detecting agricultural analytes is disclosed, including stable polymer-based sensing films such as molecular imprinted polymers (MIPs) that can be incorporated in sensors for detecting herbicides and pesticides, as well as methods of making the sensing films.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/948,888, filed Dec. 17, 2019, the entire contents ofwhich are hereby incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

Detection of agricultural analytes, particularly pesticides andherbicides, can be highly intensive and require complex equipment thatis not suited to use in the field. There exists a need for highlychemical-specific materials and easy to use sensors for detection ofcertain agricultural analytes.

BRIEF SUMMARY OF THE DISCLOSURE

Sensors and sensor components to accurately and specifically detectagricultural analytes are provided. Embodiments of the presentdisclosure relate generally to polymer-based sensors for detectingagricultural analytes, and, more specifically, to stable polymer basedsensing films such as molecular imprinted polymers (MIPs) forincorporation in sensors for detecting agricultural analytes and methodsof making the sensing films and sensors.

In one aspect, the disclosure provides a molecularly imprinted polymerfilm (MIP) that includes a crosslinking organosilane, a functionalorganosilane, a template molecule, and a porogen. According to oneembodiment, the molecular imprinted polymer is formulated as an opticaltransparent and mechanical stable thin film. According to oneembodiment, the molecular imprinted polymer is configured to detect oneor more agricultural analytes. According to one embodiment, themolecularly imprinted polymer is configured to detect one or more of aninorganic contaminant (IOC), volatile organic contaminant (VOC),synthetic organic contaminant (SOC), organic chemical, inorganicchemical, disinfection by-product, or a combination thereof. Accordingto one embodiment, the molecularly imprinted polymer is configured todetect one or more of dicamba, dichloroprop, dichloroprop-P, 2(2, 4,5-trichlorophenoxy)propionic acid, 2,4,5-trichlorophenoxyacetic acid,2,4-dichlorophenoxyacetic acid (2,4-D), or any combination thereof.

According to one embodiment, the crosslinking organosilane includestetramethoxysilane, tetraethoxysilane, trimethoxysilane,triethyoxysilane, and combinations thereof. According to one embodiment,the functional organosilane includes silanes containing amino groups andphenyl groups, preferablyn-(2-n-benzylaminoethyl)-3-aminopropyltrimethoxysilane hydrochloride,p-aminophenyltrimethoxysilane, n-phenylaminomethyltrimethoxysilane, and(aminoethylaminomethyl)phenethyltrimethoxysilane. In some embodiments,the porogen includes polar and nonpolar solvents including methanol,ethanol, isopropanol, toluene, tetrahydrofuran (THF), acetonitrile,hexane, and combinations thereof.

In another aspect, the disclosure provides a method for making amolecularly imprinted polymer for detecting agricultural analytes. Themolecularly imprinted polymer may be a film. The method includes thesteps of:

-   -   preparing a mixture of precursors comprising a crosslinking        organosilane solution and a functional organosilane solution,        water, and an acid or an base;    -   dissolving one or more agricultural analyte in a porogen to form        an agricultural analyte solution;    -   mixing the mixture of precursors and the agricultural analyte        solution with a cross-linker and, optionally, a catalyst until a        sol forms;    -   coating the sol on a pre-cleaned sensor surface;    -   drying the sol by curing the coated sensor to transform the        coated sol into a xerogel;    -   flowing methanol over the xerogel film to remove the template        molecules; and    -   flowing working buffer over the coated sensor surface for        baseline registration. Any resulting film may have a thickness        controlled by the coating speed and the concentration of sol.        According to one embodiment, the molecularly imprinted film is        configured to detect one or more of dicamba, dichloroprop,        dichloroprop-P, 2(2, 4, 5-trichlorophenoxy)propionic acid,        2,4,5-trichlorophenoxyacetic acid, and 2,4-dichlorophenoxyacetic        acid (2,4-D). According to one embodiment, the crosslinking        silane includes tetramethoxysilane, tetraethoxysilane,        trimethoxysilane, triethyoxysilane, and combinations thereof.        According to one embodiment, the functional organosilane        includes silanes containing amino groups and phenyl groups,        preferably        n-(2-n-benzylaminoethyl)-3-aminopropyltrimethoxysilane        hydrochloride, p-aminophenyltrimethoxysilane,        n-phenylaminomethyltrimethoxysilane, and        (aminoethylaminomethyl)phenethyltrimethoxysilane. In some        embodiments, the porogen includes methanol, ethanol,        isopropanol, toluene, THF, acetonitrile, hexane, and        combinations thereof.

According to one embodiment, the acid includes acetic acid, hydrochloricacid (HCl), diluted acetic acid, or diluted HCl. The base includesammonium hydroxide or sodium hydroxide. According to one embodiment, thepH of the working buffer is from about 2 to about 7. According to oneembodiment, the ratio of the crosslinking silane to the functionalsilane is from 1 to 20. According to one embodiment, the ratio of thefunctional silane to template is from 4 to 40. According to oneembodiment, the cross-linker includes tetramethoxysilane,tetraethoxysilane. trimethoxysilane, triethyoxysilane, and combinationsthereof. According to one embodiment, the mixing step is from about 5minutes to about 24 hours. According to one embodiment, the coating stepincludes dip coating, spin coating or printing (e.g., inkjet or aerosoljet). According to one embodiment, the drying step includes curing at atemperature of from about 60° C. to about 100° C. According to oneembodiment, the curing is from about 5 minutes to about 60 minutes.

These and other objects, features and advantages of the presentdisclosure will become more apparent upon reading the followingspecification in conjunction with the accompanying description, claimsand drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying Figures, which are incorporated in and constitute apart of this specification, illustrate several aspects described below.

FIG. 1 depicts an exemplary method of sol-gel synthesis of a molecularimprinted polymer according to the disclosure.

FIG. 2 shows typical sensing responses to dicamba in pH 5 acetatebuffer.

FIG. 3 shows the rate of phase change that was used to build thecalibration curve for dicamba.

FIG. 4 shows the sensing responses of an inventive film to 10 ppm ofmolecules with similar structures to dicamba: dichloroprop,dichloroprop-P, 2(2,4,5-trichlorophenoxy)propionic acid,2,4,5-trichlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid(2,4-D), 2,4-D methyl ester, and 2,4-D butyl ester.

FIG. 5 shows that the optimized molecular imprinted polymer film has nocross-reaction to citric acid.

FIG. 6 shows the effect of ionic strength in testing buffer on thedetection sensitivity.

FIG. 7 shows the results of dicamba sensing with a molecular imprintedpolymer film according to the disclosure. The arrows indicate solutionswitching.

FIG. 8 shows FTIR characterization of the prepared xerogel and the filmafter the 5 removal of template.

FIG. 9 shows SEM pictures of the molecular imprinted polymer filmsbefore (left) and after the template (right) was removed.

FIG. 10 shows the effect of different storage conditions on molecularimprinted polymer films according to the disclosure.

DETAILED DESCRIPTION

There is a great need in the art to identify technologies for detectionof certain agricultural analytes and use this understanding to developnovel sensors and sensor components to accurately and specificallydetect the chemical. The present disclosure satisfies this and otherneeds. Embodiments of the present disclosure relate generally topolymer-based sensors for detecting agricultural analytes, and morespecifically to stable polymer-based sensing films such as molecularimprinted polymers for incorporation in sensors for detectingagricultural analytes, and methods of making the sensing films andsensors.

To facilitate an understanding of the principles and features of thevarious embodiments of the disclosure, various illustrative embodimentsare explained below. Although exemplary embodiments of the disclosureare explained in detail, it is to be understood that other embodimentsare contemplated. Accordingly, it is not intended that the disclosure islimited in its scope to the details of construction and arrangement ofcomponents set forth in the following description or examples. Thedisclosure is capable of other embodiments and of being practiced orcarried out in various ways. Also, in describing the exemplaryembodiments, specific terminology will be resorted to for the sake ofclarity.

As used herein, the term “agricultural analyte” refers to any inorganiccontaminants (IOCs), volatile organic contaminants (VOCs), syntheticorganic contaminants (SOCs), organic chemicals, inorganic chemicals,small molecule compounds (e.g., low molecular weight organic compounds,sugars, amino acids, fatty acids, lipids, monosaccharides, ormetabolites), or disinfection by-products. Chemical contaminants includeall common agricultural analytes used on or around a crop such as, forexample, herbicides, pesticides, and fertilizers including, but notlimited to, auxin growth regulator based herbicides, benzoic acidherbicides, and chlorophenoxy herbicides. Specific agricultural analytecontaminants include dicamba (2-methoxy-3,6-dichlorobenzoic acid),dichloroprop, dichloroprop-P, 2(2, 4, 5-trichlorophenoxy)propionic acid,2,4,5-trichlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid(2,4-D), or any combination thereof.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,reference to a component is intended also to include composition of aplurality of components. References to a composition containing “a”constituent is intended to include other constituents in addition to theone named. In other words, the terms “a,” “an,” and “the” do not denotea limitation of quantity, but rather denote the presence of “at leastone” of the referenced item.

As used herein, the term “and/or” may mean “and,” it may mean “or,” itmay mean “exclusive-or,” it may mean “one,” it may mean “some, but notall,” it may mean “neither,” and/or it may mean “both.” The term “or” isintended to mean an inclusive “or.”

Also, in describing the exemplary embodiments, terminology will beresorted to for the sake of clarity. It is intended that each termcontemplates its broadest meaning as understood by those skilled in theart and includes all technical equivalents which operate in a similarmanner to accomplish a similar purpose. It is to be understood thatembodiments of the disclosed technology may be practiced without thesespecific details. In other instances, well-known methods, structures,and techniques have not been shown in detail in order not to obscure anunderstanding of this description. References to “one embodiment,” “anembodiment,” “example embodiment,” “some embodiments,” “certainembodiments,” “various embodiments,” etc., indicate that theembodiment(s) of the disclosed technology so described may include aparticular feature, structure, or characteristic, but not everyembodiment necessarily includes the particular feature, structure, orcharacteristic. Further, repeated use of the phrase “in one embodiment”does not necessarily refer to the same embodiment, although it may.

Ranges may be expressed herein as from “about” or “approximately” or“substantially” one particular value and/or to “about” or“approximately” or “substantially” another particular value. When such arange is expressed, other exemplary embodiments include from the oneparticular value and/or to the other particular value. Further, the term“about” means within an acceptable error range for the particular valueas determined by one of ordinary skill in the art, which will depend inpart on how the value is measured or determined, i.e., the limitationsof the measurement system. For example, “about” can mean within anacceptable standard deviation, per the practice in the art.Alternatively, “about” can mean a range of up to ±20%, preferably up to±10%, more preferably up to ±5%, and more preferably still up to ±1% ofa given value.

Where particular values are described in the application and claims,unless otherwise stated, the term “about” is implicit and in thiscontext means within an acceptable error range for the particular value.Throughout this disclosure, various aspects of the disclosure can bepresented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of thedisclosure. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6. Thisapplies regardless of the breadth of the range.

By “comprising” or “containing” or “including” is meant that at leastthe named compound, element, particle, or method step is present in thecomposition or article or method, but does not exclude the presence ofother compounds, materials, particles, method steps, even if the othersuch compounds, material, particles, method steps have the same functionas what is named.

Throughout this description, various components may be identified havingspecific values or parameters, however, these items are provided asexemplary embodiments. Indeed, the exemplary embodiments do not limitthe various aspects and concepts of the present disclosure as manycomparable parameters, sizes, ranges, and/or values may be implemented.

The terms “first,” “second,” and the like, “primary,” “secondary,” andthe like, do not denote any order, 20 quantity, or importance, butrather are used to distinguish one element from another.

It is noted that terms like “specifically,” “preferably,” “typically,”“generally,” and “often” are not utilized herein to limit the scope ofthe claimed disclosure or to imply that certain features are critical,essential, or even important to the structure or function of the claimeddisclosure. Rather, these terms are merely intended to highlightalternative or additional features that may or may not be utilized in aparticular embodiment of the present disclosure. It is also noted thatterms like “substantially” and “about” are utilized herein to representthe inherent degree of uncertainty that may be attributed to anyquantitative comparison, value, measurement, or other representation.

It is also to be understood that the mention of one or more method stepsdoes not preclude the presence of additional method steps or interveningmethod steps between those steps expressly identified. Similarly, it isalso to be understood that the mention of one or more components in acomposition does not preclude the presence of additional components thanthose expressly identified.

The materials described hereinafter as making up the various elements ofthe present disclosure are intended to be illustrative and notrestrictive. Many suitable materials that would perform the same or asimilar function as the materials described herein are intended to beembraced within the scope of the disclosure. Such other materials notdescribed herein can include, but are not limited to, materials that aredeveloped after the time of the development of the disclosure, forexample. Any dimensions listed in the various drawings are forillustrative purposes only and are not intended to be limiting. Otherdimensions and proportions are contemplated and intended to be includedwithin the scope of the disclosure.

Films and Sensors of the Disclosure

The films and sensors of the disclosure are adapted to detect thepresence of agricultural analytes. An exemplary agricultural analytethat can be detected using the films and sensors as provided hereinincludes the herbicide, dicamba. Dicamba, 3,6-dichloro-2-methoxybenzoicacid, is classified as either a benzoic acid or chlorophenoxy herbicide.Dicamba is a selective herbicide used to control a wide spectrum ofbroadleaf weeds and woody plants in various crops, pastures, and turfgrass. Dicamba has long been one of the most widely used selectiveherbicides due to its high efficiency and low toxicity. The introductionof dicamba-resistant genetically modified plants (soybean and cotton) byMonsanto also promoted an increased use of dicamba worldwide. Some U.S.states have, however, banned the sale and use of dicamba because offarmers complaints of drift and damage to nonresistant crops. To monitorthe dicamba drift to nonresistant crops, a rapid and sensitive methodfor dicamba detection is desired. Such methods as provided herein andincludes the use of a molecularly imprinted polymer that is incorporatedinto a sensor and specifically binds to an agricultural analyte such asdicamba. The methods as provided here also extend to all agriculturalanalytes by adaption of the molecular imprinted polymer such that themolecular imprinted polymer is configured or otherwise adapted to bindto or otherwise detect a target agricultural analyte.

Exemplary sensors that can be combined with molecular imprinted polymersand films thereof include interferometric sensors based on a planaroptical waveguide. This transduction platform can detect a wide varietyof chemical compounds by monitoring changes in refractive index in aselective, concentrating sensing film. At the heart of the device is theplanar optical waveguide with an evanescent field sensitive to changesin the volume immediately above the surface. Optically combining aguided sensing beam with a reference beam generates an interferencefringe pattern whose phase changes in proportion to index of refractiondifferences between the two arms of the interferometer. Applying achemically selective film over the sensing arm of the interferometerprovides the basis for a chemical sensor.

Polymer-based sensing films include hydrogels, molecular imprintedpolymers, conducting polymers, and polymer composites. Polymer-basedsensing films have been developed to enhance the performance of sensorsand biosensors. The diverse polymer chemistries can be easily modifiedto fine-tune their binding selectivity, reusability, biocompatibility,and long-term stability. Typically, the polymer-based sensing materialscontain functional molecules (groups) to capture target molecule, andthree-dimensional polymeric matrices to immobilize the functionalmolecules (groups). Molecular interactions between the analyte and thepolymer sensing film are typically used for sensing film design. Theinteraction can either be physical (via adsorption or swelling),chemical (via reaction of sensing film and target), or biological (viacomplementary molecular recognition events like DNA binding orreceptor/guest interactions in biomolecules). For the chemicals withlower reactivities such as BTEX (benzene, toluene, ethylbenzene andxylene), physical interactions between the analyte and sensing filmincluding adsorption or swelling based sensing films are typically used.For chemicals containing unique functional groups, binding chemistriesincluding hydrogen bonding, acid/base interactions, charge-transferinteractions including π-π stacking, complexation etc. are used todevelop selective sensing films.

Molecular imprinted polymers are one type of polymer-based sensing filmand are synthetic analogues to natural biological antibody-antigensystems. Molecular imprinted polymers potentially offer the specificityand selectivity of the biological receptors with the explicit advantagesof durability with respect to environmental conditions and low cost. Forexample, polymer-based molecular imprinted polymers commonly do notrequire special environmental storage and can be applied over a muchwider temperature range. Molecular imprinting may be prepared with asolution containing a template (target) molecule, a functional monomer,a cross-linker, a polymerization initiator dissolved in an appropriatesolvent. The role of the functional monomer is to form a complex withthe template by providing binding sites for one or more agriculturalanalytes. The role of cross-linker is to link functionalmonomers-template complex to a highly cross-linked polymer. Thepolymerization is initiated to produce molecular assemblies with thepolymer chains arranging themselves around the template molecule. Theremoval of the templates creates analyte-selective binding moietieswithin the polymer matrix. The majority of molecular imprinted polymersare based on organic polymers synthesized via polymerization fromfunctional and crosslinking monomers containing vinyl or acrylic groups.According to one embodiment, the molecular imprinted materials can beused in an aqueous environment.

Organosilane based sol-gel chemistry can immobilize the functionalmolecules inside the polymer matrix for selective binding ofagricultural analytes due to diverse silanization chemistries. In thesol-gel process, monomers are converted into a colloidal solution (sol)that acts as the precursor for an integrated network (or gel) of eitherdiscrete particles or network polymers. Sol-gel is a simple, stable andcost-effective method for the production of homogeneous inorganicpolymer network.

As illustrated in FIG. 1 , inorganic siloxane bonds may be formed viaacid or alkali catalyzed hydrolysis and condensation of a series ofsilane monomers. Sol then gradually evolves towards the formation ofgel-like three-dimensional polymer network. Enclosure of a templateagricultural analyte molecule (e.g., dicamba) results in the formationof imprinted media.

Agricultural analyte can be targeted for sensing film design. Hydrogenbonding, charge-transfer complexation, and π-π interaction can be usedfor selection of functional molecules. Tetramethoxysilane (TMOS) andtetraethoxysilane, and combinations thereof, may be selected as possiblecross-linking silanes. Silanes containing amino groups and phenyl groupscan be suitable functional silanes, including but not limited ton-(2-n-benzlkaminoethyl)-3-aminopropyltrimethoxysilane hydrochloride,p-aminophenyltrimethoxysilane, n-phenylaminomethyltrimethoxysilane,(aminoethylaminomethyl)phenethyltrimethoxysilane, or combinationsthereof. In some embodiments, the silanes include crosslinking silanes,functional silanes, or combinations thereof.

Exemplary crosslinking silanes include, but are not limited to,tetramethoxysilane and tetraethoxysilane, or combinations thereof.Exemplary functional silanes include, but are not limited to, silanescontaining amino groups and phenyl groups, preferablyn-(2-n-benzylaminoethyl)-3-aminopropyltrimethoxysilane hydrochloride,p-aminophenyltrimethoxysilane, n-phenylaminomethyltrimethoxysilane,(aminoethylaminomethyl)phenethyltrimethoxysilane, or combinationsthereof.

In some embodiments, the ratio of the crosslinking silane to thefunctional silane is from 0.5 to 40. In some embodiments, the ratio ofthe crosslinking silane to the functional silane is from 0.75 to 30. Insome embodiments, the ratio of the crosslinking silane to the functionalsilane is from 1 to 20.

In some embodiments, the ratio of the functional silane to agriculturalanalyte template is from 1 to 160. In some embodiments, the ratio of thefunctional silane to agricultural analyte template is from 2 to 120. Insome embodiments, the ratio of the functional silane to agriculturalanalyte template is from 3 to 80. In some embodiments, the ratio of thefunctional silane to agricultural analyte template is from 4 to 40.

Once the sol is formed by mixing the agricultural analyte, the silanes,and optionally a porogen for about 1 minutes to about 48 hours.According to another embodiment, the mixing time is from about 3 minutesto about 36 hours. According to another embodiment, the mixing time isfrom about 5 minutes to about 24 hours.

The sol can be coated onto a pre-cleaned sensor by any number of methodsknown in the art, including dip coating, spin coating or printing (e.g.,inkjet or aerosol jet) the sol onto the sensor. The sol can then bedried by curing the coated sensor to transform the coated sol into axerogel. Methanol can be flowed over the xerogel film to remove thetemplate molecules, followed by flowing working buffer over the coatedsensor surface for baseline registration. In some embodiments, theworking buffer has a pH of 0.5 to 9. In some embodiments, the workingbuffer has a pH of 1 to 8. In some embodiments, the working buffer has apH of 2 to 7.

In some embodiments, the curing is performed at a temperature of fromtypically about room temperature to typically about 100° C. In someembodiments, the curing is performed at a temperature of from about 60°C. to about 80° C. In some embodiments, the curing is performed at atemperature of from about 70° C. to about 80° C. In some embodiments,the curing is performed at a temperature of about 75° C.

In some embodiments, the curing time is from about 1 minute to about 180minutes. In some embodiments, the curing time is from 2.5 minutes toabout 120 minutes. In some embodiments, the curing time is from about 5minutes to about 60 minutes.

In some embodiments, the molecular imprinted polymers is configured tospecifically detect dicamba. In some embodiments, the molecularimprinted polymer is configured to detect dicamba or one or more relatedcompounds such as, for example, dichloroprop, dichloroprop-P, 2(2, 4,5-trichlorophenoxy)propionic acid, 2,4,5-trichlorophenoxyacetic acid,2,4 dichlorophenoxyacetic acid (2,4-D) or combinations thereof.

The sensitivity and selectivity of the molecular imprinted polymer canbe manipulated by one or more of the following. According to oneembodiment, the molar ratio of the template molecule (agriculturalanalyte) to functional molecules inside the molecular imprinted polymercan be fine-tuned, with an exemplary molar ratio of from 1 to 160.According to one embodiment, the molar ratio of the template molecule tofunctional molecules inside the molecular imprinted polymer is from 2 to120. According to one embodiment, the molar ratio of the templatemolecule to functional molecules inside the molecular imprinted polymeris from 5 to 40.

The selection of the porogen can affect the molecular imprinted polymer.According to one embodiment, the porogen can be a polar solvent (e.g.,acetonitrile or methanol), a non-polar solvent (e.g., hexane ortoluene), and mixtures of polar and non-polar solvents. The hydrolysistime of silane molecules can also be optimized, as well as performingthe hydrolysis with a catalyst and/or without a catalyst. The hydrolysiscan be performed for a period of from about 5 minutes to about 36 hours.According to another embodiment, the hydrolysis can be performed for aperiod of from about 2 hours to about 24 hours. According to anotherembodiment, the hydrolysis can be performed for a period of from about 2hours to about 18 hours.

The catalyst that can be used with the hydrolysis can be an acid (e.g.,HCl or dilute HCl) or a base (ammonium hydroxide or sodium hydroxide.The addition of a catalyst and type of catalyst depends on the speed ofthe sol formation, such that the hydrolysis occurs at a rate sufficientto form the sol but not so fast that the sol becomes a gel (which may bedifficult to coat on the chip). The temperature selected for xerogelformation (e.g., solvent drying temperatures) can alter the molecularimprinted polymer properties, and can include temperatures ranging fromambient or room temperature to about 100° C. The time for xerogelformation can be from about 1 minute to about 180 minutes. According toanother embodiment, time for xerogel formation can be from about 2minutes to about 120 minutes. According to another embodiment, time forxerogel formation can be from about 5 minutes to 60 minutes. Theseparameters, alone or in any combination, can be adjusted to improve thedetection sensitivity and selectivity of the resulting molecularimprinted polymer.

The stability of the molecular imprinted polymer sensing film can alsobe improved by adjusting the molar ratio of template molecule tofunctional molecule inside the molecular imprinted polymer, theselection of porogen (e.g., a polar solvent such as acetonitrile ormethanol, a non-polar solvent such as hexane or toluene, and mixtures ofpolar and non-polar solvents), and the storage conditions. Molecularimprinted polymer prepared with high ratios of functional molecule totemplate molecule produces molecular imprinted polymer that can beformulated as films with superior stability compared to polymersprepared with low ratios of functional molecule to template molecule.The stability of the molecularly imprinted polymer sensing film may beimproved by storing the molecular imprinted polymer film in liquids withlower surface tension.

The molecular imprinted polymer can be incorporated into a sensor, suchas for example and not limitation an interferometric sensor, anelectrochemical based sensor, a surface plasmon based sensor, and aquartz crystal microbalance based sensor. This sensor can be combinedwith a detection system in order to detect the presence of anagricultural analyte in a variety of different environments, such as,for example, agricultural products (e.g., to detect agricultural analytedrift), food preparation systems (to detect agricultural analytecontamination), and monitoring agricultural analyte residue fromsprayers or other delivery means. A sensor that is particularly usefulwith the molecular imprinted polymers described herein is found in U.S.application Ser. No. 16/454,789 filed Jun. 27, 2019 (incorporated byreference herein in its entirety).

According to a particular embodiment, a sensor and detection system isprovided that can be configured to distinguish between chemical analytesvia the molecular imprinted polymers described herein.

EXAMPLES

The present disclosure is also described and demonstrated by way of thefollowing examples. The use of these and other examples anywhere in thespecification is illustrative only and in no way limits the scope andmeaning of the disclosure or of any exemplified term. Likewise, thedisclosure is not limited to any particular preferred embodimentsdescribed here. Indeed, many modifications and variations of thedisclosure may be apparent to those skilled in the art upon reading thisspecification, and such variations can be made without departing fromthe disclosure in spirit or in scope. The disclosure is therefore to belimited only by the terms of the appended claims along with the fullscope of equivalents to which those claims are entitled.

Example 1 Synthesis of a Dicamba-Based Molecular Imprinted Polymer

Dicamba contains a benzene ring and a carboxylic acid group, which canbe targeted for sensing film design. Hydrogen bonding, charge-transfercomplexation and π-π interaction can be used for selection of functionalmolecules. Tetramethoxysilane (TMOS) was selected as the cross-linkingsilane. A variety of silanes containing amino groups and phenyl groupswere examined as the functional silanes. The amounts of monomers,hydrolysis speed, temperature and amount of porogen (i.e., organicsolvents or water in aqueous preparations) can be used to determine andoptimize the morphology of the polymer.

Materials

Tetramethoxysilane (TMOS), N-phenylaminopropyltrimethoxysilane,N-(2-N-benzylaminoethyl)-3-aminopropyltrimethoxysilane,p-aminophenyltrimethoxysilane, N-phenylaminomethyltrimethoxysilane,(aminoethylaminomethyl)phenethyltrimethoxysilane were obtained fromGelest (Morrisville, PA). Dicamba (Sigma-Aldrich Chemical Co. St. Louis,MO) was used as a template. Chemicals including 2,4-D, citric acid,2,4-D methyl ester, 2,4-D butyl ester, methanol, toluene andhydrochloric acid were obtained from Sigma-Aldrich (St. Louis, 15 MO).All chemicals were used as received.

Preparation of Sol-Gel Molecularly Imprinted Polymer

Dicamba was first dissolved in methanol and then diluted to toluene.Different ratios of silanes and acid were added to the dicamba solutionand the whole mixture was stirred at room temperature overnight. The solwas formed when the reaction was completed. A thin film of sol wascoated on a cleaned waveguide sensor using a house-made dip coater. Thecoated film was cured at room temperature to 100° C. for about 5 minutesto about 60 minutes to obtain a transparent xerogel. The film thicknesscan be adjusted by changing the dipping rate and the concentration ofsol. The coated chip was then placed in a flow cell. Methanol was flowedover the chip at a rate of 2 ml/min for 1 hour to remove the template.The prepared xerogel and the film after the removal of template werecharacterized using FTIR to determine the molecular imprinted polymersmolecular composition and structure.

As shown in FIG. 8 , the peaks at 1140 and 1030 cm⁻¹ were assigned toC—O stretching vibration mode of Si—O—CH₃ and the stretching mode ofSi—O—Si while the peak at 2849 cm⁻¹ was the C—H stretching vibration andbending vibration mode of Si—O—CH₃. All these peaks were attributed toTMOS. Peaks at 1604 and 1495 cm⁻¹ were assigned to C—C stretches inaromatic 30 ring from the functional molecules. The peak at 1738 cm⁻¹was from the carbonyl functional group from the template molecule. TheFTIR study indicated that the matrix molecules, functional molecules andtemplate molecules were fully integrated in the molecular imprintedpolymer xerogel. After the template was removed, the peak at 1738 cm⁻¹was reduced dramatically.

Sensor Testing

A dicamba stock solution was prepared by dissolving a known amount ofdicamba in methanol. A series of dilution was conducted to make dicambastandards with concentrations of 0.1 ppm to 10 ppm in a testing buffer.HCl and NaOH were used to adjust the pH of the testing buffer. NaCl wasadded to the testing buffer to investigate the effect of ionic strengthon the sensing performance. A peristaltic pump was used to deliver thetesting solution into the flow cell at 2 ml/min. The baseline wasregistered first with a testing buffer for 4 minutes and then dicambasolution was delivered over waveguide surface for another 5 minutes toregister a sensing response. The waveguide surface was flushed withtesting buffer at the end of the sensing assay so all the attacheddicamba molecules were removed and the sensing surface was ready foranother measurement. The entire sensing response was completed in 15minutes.

Interference compounds including citrate, 2,4-D esters were prepared inthe same testing media and used for specificity characterization.

Results and Discussion

Fresh made molecular imprinted polymer was tested with dicamba solutionsprepared in 0.1M acetate buffer with pH 5 and each solution was testedfour times for the reproducibility study. As FIG. 2 showed, themolecular imprinted polymer film was responsive to dicamba and as low as0.5 ppm of dicamba can be detected. The sensing response was reversibleindicating the film can be reused. In addition, the sensingreproducibility was within 10%. A calibration curve may be constructedusing either absolute phase change (plateau of the sensing curve) of therate of phase change (slope of the sensing curves), as shown in FIG. 3 .The rate of phase change was preferred for calibration curve becausethis rate is less influenced by the bulk refractive change caused bymatrix change. The same molecular imprinted polymer was tested forsensing selectivity. Molecules with similar structures were testedincluding dichloroprop, dichloroprop-P, 2(2, 4,5-trichlorophenoxy)propionic acid, 2,4,5-trichlorophenoxyacetic acid,citric acid, 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4-D methylester, 2,4-D butyl ester.

The sensing responses to 10 ppm of each molecule is shown in FIG. 4 .The molecular imprinted polymer did not respond to esters but crossreacted to all organic acids including citric acid. To improve thesensing selectivity, molar ratios of cross-linking monomer to functionalmonomer (1 to 20) and functional molecules to templates (4 to 40) wereexamined along with the pH of the testing buffer (pH 2 to pH 7). Theoptimized molecular imprinted polymer film has no cross-reaction tocitric acid as shown in FIG. 5 .

To optimize the detection sensitivity, the effect of ionic strength ofthe testing buffer was investigated, with ionic strengths ranging fromranging from 10 mM to 1 M. It was observed that a better detectionsensitivity can be obtained for the testing media with a lower ionicstrength as shown in FIG. 6 . Although 10 mM of ionic strength providedalmost two-fold increased detection response compared to those obtainedin 50 mM buffer, the ionic strength of 50 mM was selected for itsenhanced buffer strength. The molecular imprinted polymer was tested fora series of dicamba in 50 mM pH 2 buffer. The sensing responses areshown in FIG. 7 . The film was sensitive. As low as 0.1 ppm of dicambawas detected.

Because the voids inside the molecular imprinted polymer were used forherbicide sensing, maintaining the porous structures inside themolecular imprinted polymer was important for providing a stable andreproducible sensing response over time. The impact of molecularimprinted polymer compositions, processing procedures and storageconditions on the stability of sensing film over a long period wasdetermined. The shelf life of the molecular imprinted polymer sensingfilm was influenced by the composition of the molecular imprintedpolymer and the storage conditions. Improper molecular imprinted polymercompositions and storage conditions could cause a collapsed porousstructure inside the molecular imprinted polymer films after thetemplate molecules were removed, which resulted in reduced sensingcapabilities. A scanning electron microscope (SEM) was used to examinethe porous structure of the molecular imprinted polymer and filmsthereof. FIG. 9 shows SEM pictures of the molecular imprinted polymerfilms before (left) and after the template (right) was removed. The lossof this porous structure can be clearly seen for molecular imprintedpolymers prepared with improper compositions and/or storage conditions.

Molecular imprinted polymer with a higher molar ratio of functionalmolecules to template molecules produced a stable sensing film comparedto the molecular imprinted polymers with a lower molar ratio. Inaddition, the shelf life of the molecular imprinted polymer was improvedby storing the film in liquids with lower surface tensions (e.g.,methanol). The stability results can be found in FIG. 10 .

While several possible embodiments are disclosed above, embodiments ofthe present disclosure are not so limited. These exemplary embodimentsare not intended to be exhaustive or to unnecessarily limit the scope ofthe disclosure, but instead were chosen and described in order toexplain the principles of the present disclosure so that others skilledin the art may practice the disclosure. Indeed, various modifications ofthe disclosure in addition to those described herein will becomeapparent to those skilled in the art from the foregoing description.Such modifications are intended to fall within the scope of the appendedclaims.

What is claimed is:
 1. A molecularly imprinted polymer in the form of axerogel film, the molecularly imprinted polymer comprising: acrosslinking organosilane; a functional organosilane; a templatemolecule and a porogen; wherein the molecularly imprinted polymer in theform of a xerogel film is configured to detect one or more agriculturalanalytes.
 2. The molecularly imprinted polymer of claim 1, wherein theagricultural analyte is one or more of an inorganic contaminant (IOC),volatile organic contaminant (VOC), synthetic organic contaminant (SOC),organic chemical, inorganic chemical, disinfection by-product, or acombination thereof.
 3. The molecularly imprinted polymer of claim 1,wherein the agricultural analyte is one or more of dicamba,dichloroprop, dichloroprop-P, 2(2, 4, 5-trichlorophenoxy)propionic acid,2,4,5-trichlorophenoxyacetic acid, and 2,4-dichlorophenoxyacetic acid(2,4-D).
 4. The molecular imprinted polymer of claim 1, wherein thecrosslinking organosilane comprises tetramethoxysilane,tetraethoxysilane, trimethoxysilane, triethoxysilane or combinationsthereof.
 5. The molecular imprinted polymer of claim 1, wherein thefunctional organosilane comprisesn-(2-n-benzylaminoethyl)-3-aminopropyltrimethoxysilane hydrochloride,p-aminophenyltrimethoxysilane, n-phenylaminomethyltrimethoxysilane,(aminoethylaminomethyl)phenethyltrimethoxysilane, or combinationsthereof.
 6. The molecular imprinted polymer of claim 1, wherein theporogen comprises methanol, ethanol, isopropanol, toluene, THF,acetonitrile, hexane, or combinations thereof.
 7. The molecularimprinted polymer of claim 1, having a ratio of the crosslinkingorganosilane to the functional organosilane of 1 to
 20. 8. The molecularimprinted polymer of claim 1, having a ratio of the functionalorganosilane to the template molecule of 4 to
 40. 9. The molecularlyimprinted polymer of claim 1, wherein the molecularly imprinted polymerin the form of a xerogel film is incorporated in an interferometricsensor.